I have been setting up a new install.  I was set up with 2x 1TB drives.  One of them physically broke while I was squeezing a bunch of other drives into the very small case I have.  I have 2x 3TB drives I am trying to add.  When I try to choose one of the 3TB drives as the parity drive I am getting a message saying it is the wrong disk.  If I try to select the existing 1TB it says that it is not the largest drive.  I don't have another 1TB drive.  It does allow me to select one of the 3TB as parity.  My question is: if I choose the 3TB as my parity, am I going to lose the data that is on the 1TB parity drive?

There is no ‘data’ on a parity drive.   What there is the information that works in conjunction with all the data drives to work out what should be on a missing/failed drive.

 

if you had the special case of 1 data drive and one parity drive then they will be mirror images of each other.   If this is where you are coming from then you can create a new array from the existing 1TB drive plus the 3TB drives (with one of them as parity).    If that is not your position then you need to provide more information.